The invention relates to a planar filter for plug-in connectors having a multiplicity of signal pins to be connected that are disposed in rows and columns, a carrier which has an opening for each of the signal pins, and a capacitor in the vicinity of each of the openings with a first layer connected to an assigned signal conductor, a second layer for connection to ground and a dielectric in the form of a layer between the first layer and the second layer. The invention also relates to a multi-pole angle-connecting device with a planar filter.
In the case of multi-pole plug-in connectors, which are used for the transmission of digital or analog measuring signals from multi-function measuring devices or in high-speed transmission of information, there is the necessity for filtering in order to filter out interference signals that are introduced. That filtering-out of interference signals which are introduced generally takes place with capacitors, of which there is one provided for each line carrying a signal. For that purpose, the capacitors are advantageously combined into planar filters and inserted into the plug-in connectors. The planar filters are passed through by the signal conductors and there is at least one capacitor provided for each of the signal conductors. The capacitors are disposed on a carrier, that is generally formed of alumina. French Patent 2 422 268 describes such a plug-in connector with filtering for each connector pin. The connectors are inserted in a ceramic sheet provided with holes and are carried by that sheet. Each capacitor configuration includes a small dielectric ceramic sheet, which for its part is provided on one side with grounding electrodes that are provided throughout the surface with the exception of regions of the pin lead-throughs, and on the other side with insular signal electrodes which are electrically connected to the connector pins. The coating of the electrodes takes place, as is known from U.S. Pat. No. 4,007,296, by the screen-printing process, with the customary pastes based on noble metals (including palladium among others). The grounding electrodes change into lateral metallizations, which are connected to the metallic housing and represent a ground discharge for the capacitors of the signal electrodes to the connector housing, and then on to the connected device. Another filter is formed by either a ground electrode with clearances for the connector pins or a number of signal electrodes corresponding to the number of connector pins being applied to the carrier. A dielectric layer is applied on top thereof and finally the other electrode layer, that is to say the number of signal electrodes corresponding to the number of connector pins or a ground electrode with clearances for the connector pins, is applied on top thereof (see European Patent 0 124 264, U.S. Pat. No. 3,267,342 and U.S. Pat. No. 3,544,434). That configuration is then protected from external influences by a coating of a resistant material, for instance a lacquer. However, in that case too the carrier is formed by an alumina material, to which the electrodes are applied, generally through the use of a screen-printing technique, with a dielectric layer lying between. In the case of those filters, the conductive layers and the dielectric layers are applied in the manner of a xe2x80x9csandwichxe2x80x9d through the use of a screen-printing technique, which causes problems in terms of the dielectric strength due to the thin dielectric layers. Since neighboring signal electrodes are disposed at only a small distance from one another, a capacitive coupling through unavoidable cross-capacitances cannot be ruled out. That coupling is extremely minor. However, in the case of the known planar capacitors, the mutually facing end surfaces of the signal electrodes are extremely small because of their small layer thickness and the layer thicknesses of the dielectric layers are similarly extremely small, so that the resultant cross-capacitance is extremely small and the problem of crosstalk becomes insignificant. The production of such planar filters also requires an alternating application of metallic layers and dielectric layers and is therefore (relatively) complex. Furthermore, such planar filters lack dielectric strength. In order to improve the dielectric strengths, thicker dielectric layers are necessary. Then, however, the cross-capacitances that are decisive for a coupling assume values which no longer rule out crosstalk. Such a configuration, with capacitors of high dielectric strength formed as classic sheet capacitors, in which the parasitic capacitances can form and in certain cases can disturb signal transmission, is described in German Utility Model 297 12 001.8.
It is accordingly an object of the invention to provide a planar filter and a multi-pole angle-connecting device with a planar filter, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, in which parasitic capacitances between signal electrodes are suppressed while maintaining dielectric strength, which can be produced cost-effectively and easily and which can be used reliably.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a plug-in connector having signal conductors, a multiplicity of signal pins to be connected, the signal pins disposed in rows and columns, and a carrier having openings formed therein each for receiving a respective one of the signal pins, a monolithic planar filter, comprising capacitors each disposed in the vicinity of a respective one of the openings, the capacitors each having a first layer connected to an assigned one of the signal conductors, a second layer for connection to ground, and a dielectric carrier in the form of a layer disposed between the first and second layers, the carrier having two side surfaces, an edge and pin lead-throughs for the signal pins, and the carrier formed of a mass with a relatively high dielectric constant shaped into a block, perforated and subsequently sintered and ground; the ground electrode applied to and entirely areally covering one of the side surfaces of the carrier apart from the pin lead-throughs and a directly surrounding area, and the signal electrodes applied to the other of the side surfaces of the carrier, extending from the pin lead-throughs and forming insular regions extending substantially from the signal pins to the edge of the carrier.
According to the invention, the planar filter has a monolithic structure and the carrier is a mechanically inflexible and rigid layer of a ceramic mass with a relatively high dielectric constant.
In accordance with another feature of the invention, ceramic masses which are suitable are those with a dielectric constant of not less than 5,000. Such masses are, for example, barium titanate masses. The dielectric constant is advantageously greater than 10,000.
The plate which is formed from this mass is provided with the holes necessary for leading through the signal pins, fired and sintered. After the thermal treatment, the plate which is thus obtained is ground to achieve planarity. The thickness of the carrier in this case ensures its dielectric strength. The capacitors for each of the pin lead-throughs are formed by signal electrodes assigned to them and a ground electrode.
One side of this sheet of the ceramic carrier that is prepared in this way bears the ground electrode and the other side is provided with the signal electrodes of the capacitors, which is applied with conductive printing pastes by screen printing. In this case, the ground electrode can be led at least up to one of the outer narrow sides of the carrier, for establishing a connection to the ground-housing of the plug-in connector.
Each signal electrode which surrounds a lead-through opening for the assigned connector pin may have been led into the lead-through, which provides an improved possibility for soldering with the connector pin concerned. Since the ground electrode covers the entire surface area of one of the side surfaces of the carrier, apart from the locations where the signal pins penetrate and their directly surrounding area, good shielding is achieved. The signal electrodes disposed on the other side surface of the carrier form insular regions, which extend from the locations where the signal pins penetrate, essentially surround the signal-pin lead-through and extend laterally to the edge of the carrier.
In accordance with a further feature of the invention, in order to obtain as smooth a surface as possible and consequently precisely defined electrical conditions, both side surfaces are lapped to planarity before applying the layers of the capacitors. This surface, which is thus particularly smooth and level, ensures a field-strength distribution undisturbed by deviating geometrical conditions.
Since the individual signal electrodes are opposite one another merely at their end surfaces, which account for negligible proportions of the surface area, the parasitic capacitances causing a capacitive coupling between the signal conductors are also negligible. As a result, a capacitive coupling due to cross-capacitances or parasitic capacitances is at least reduced, if not ruled out entirely, so that crosstalk phenomena during analog transmissions are suppressed.
In accordance with an added feature of the invention, a ceramic on a titanate basis is advantageously provided as the mass for this dielectric. Titantates of alkaline earth metals, for instance barium, strontium or a mixture thereof, are used in particular therefor. These masses, sintered as ceramic, have adequate mechanical strength and have higher dielectric constants, so that the desired capacitances can be achieved even with greater thicknesses of the carrier.
With the objects of the invention in view there is also provided a multi-pole angle-connecting device, comprising the signal conductors each being continuous, assigned to a respective pole and disposed in a configuration; the lead-through openings in the carrier of the planar filter disposed in a configuration; a supporting plate, particularly in the form of a printed circuit board, having soldering points and lead-through openings in a configuration corresponding to one of the configuration of the lead-through openings and the configuration of the signal conductors; and the planar filter according to claim 1 having a side to be soldered onto and areally supported by the supporting plate; the signal conductors each having one end to be soldered to a corresponding one of the soldering points and another end constructed as one of a connector pin and a plug-in socket.
Therefore, in one application, this planar filter is supported by a supporting plate, which is disposed so as to lie areally against one of the two sides of the planar filter. Application on the side on which mechanical stresses are to be expected is advantageous. The supporting plate, which is an insulating printed circuit board or a preferably ceramic substrate sheet, has the same pattern of holes for the signal conductors which are to be led through as the planar filter. These lead-throughs are metallized, at least in the region of one end surface, so that the signal conductors can be securely soldered to the supporting plate. In this case, the metallization leads into the lead-through, so that the contact points of the signal electrodes of the planar filter are included in soldering by solder drawn through by capillary action, so that the planar filter is included and brought into electrical contact by one soldering operation.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a planar filter and a multi-pole angle-connecting device with a planar filter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.